While prompt administration of thrombolytic therapy reduces mortality from myocardial infarction, some 20% of patients fail to respond to this treatment. This project will use an in vitro model of the human lytic-resistant thrombus to investigate a key issue: African-Americans treated with recombinant tissue plasminogen activator (rt-PA) for myocardial infarctions had higher vessel patency rates than Caucasians, yet at the cost of increased bleeding problems.